President Obama’s appallingly tepid response to the Paris slaughter makes him an outlier in a world suddenly determined to crush the Islamic State barbarians. In one of the worst appearances ever by an American president during a crisis, Obama, meeting in Turkey with other heads of state, called the atrocity a “setback” and urged patience.

Even after French President François Hollande gave a rousing speech to Parliament, declaring, “We are in a war against jihadist terrorism, which is threatening the whole world,” and urged Obama to join a coordinated effort, the president said no.

“It’s best that we don’t, you know, shoot first and aim later,” Obama said.

So much for solidarity with the French. Like Herman Melville’s character in “Bartleby, the Scrivener,” Obama would “prefer not to.” But passive resistance is not a viable strategy against medieval madmen.

Obama did show one streak of passion — while denouncing as ­“un-American” calls to block Syrian refugees from being resettled in the US. Thus he got animated only to denounce other Americans, a strange thing for an American president to do on foreign soil.

Then again, there is nothing new about it. The greater the crisis, the smaller Obama is. He is what is strange.

His reaction to Paris, coupled with his appeasement of Iran and foolish refusal even to call Islamic terrorism what it is, proves once and for all that he is the weak link in the most important calling of our time. This is World War III, and the free West is under attack, just as it was during the first two world wars.

Imagine if Obama had been president during those watershed events.

Had he been commander in chief during the First World War, the Germans would have prevailed. If it had been Obama instead of FDR and Truman leading the allies against the Nazis and Japanese, the West would have lost.

Speaking of that era’s leaders, imagine Winston Churchill’s reaction to Obama’s dithering in the face of jihadist terror.

If Obama had been president instead of Abraham Lincoln in the Civil War, there probably wouldn’t be a United States. The union would have been dissolved without a fight, and slavery might have survived another 50 years.

Those are the contexts that give meaning to Obama’s refusal to lead the war against the Islamic State. In any of the major confrontations in our history, Obama would have been the wrong man for the job.

As he is now.

Against the savagery we saw in Paris, there is only one moral response. It is neither wise nor virtuous to expect that the enemy will voluntarily lay down its arms. Even Pope Francis has suggested we are experiencing a Third World War, “one fought piecemeal, with crimes, massacres, destruction.”

Time is not on our side. The cancer on humankind is spreading, and it must be defeated as soon as possible.

The urgency is revealed by potential future scenarios. Imagine there is a Paris-like attack in New York, Washington, DC, or Chicago in coming weeks.

Would Obama finally rethink his approach? Would his security team be sorry they hadn’t urged him to do more? Would Democrats in Congress regret that they put loyalty to him ahead of all else?

The same challenge goes to all Americans. Who among us could say we did everything within our power to protect the nation before it was too late?

The questions matter because there is a growing belief in law enforcement that a successful attack on the homeland is likely, maybe even inevitable.

In normal times, the country rallies around the president in emergencies. But we are not living in normal times and Obama is approaching the point of zero credibility on national security. There is no sign that he grasps the significance of what happened in Paris and will not change course.

Contrast that with others in positions of responsibility. Police Commissioner Bill Bratton rolled out a new critical-response team, saying, “Our first response is to try by the speed of our actions to save as many lives as possible, which means taking them out before they kill others.”

Even the mayor of Washington, DC, is ramping up security.

Then there’s Russia, which, after conceding that one of its commercial airliners was brought down over Egypt by a bomb placed on board, is vowing a fierce campaign against the Islamic State. “We will find them anywhere on the planet and punish them,” Vladimir Putin said yesterday. None can doubt he means it.

As for Obama, the only obvious course is to doubt that he will keep America safe.

‘Server’ right? Unlikely

Reader Bill Bousquette has a dream — that the FBI will honestly investigate Hillary Clinton’s email scandals because Director James Comey is a straight shooter.

He cites Comey’s willingness to contradict President Obama on rising murder rates, and his threat to resign from the Bush administration over what he regarded as an ethical issue.

“I agree that the Obama Justice Department will not indict Clinton even if the FBI believes a crime was committed,” Bousquette writes. “But there is more than even chance Comey would resign then. Politically, that would be almost as impactful as an indictment.”

Granted, it’s a very nice dream.

2 parties a-‘greed’

New Yorkers asked for bipartisanship in Albany, and the request has been granted.

With the former heads of both parties in both houses simultaneously on trial for corruption, the eureka moment has arrived.

One hitch — it’s only thanks to prosecutors.

Next time, voters should be more specific.

City’s study is as crazy as it $eems

When you’re a hammer, the whole world is a nail. Witness City Hall’s finding that New York is chock full of depressive types and other head cases.

The results of a Health Department study, that one in five New Yorkers have a mental health disorder, sound suspiciously convenient. First lady Chirlane McCray has made improving access to treatment a priority, and her husband is rolling out a series of programs to that end.

The timing suggests the study was crafted to support a policy decision already made.

Shouldn’t the study come before the programs are created? Do doctors first prescribe medication, then give you an exam?

McCray said she and her parents suffered from depression, and complained that she had trouble finding help for her daughter, who also had substance-abuse problems.

A year ago, McCray argued that “the mental health system is broken.” That’s liberal code signaling sweeping and expensive changes.

The idea would be admirable if it focused on the most critical problems — getting the crazies off the streets. They are a danger to others, as well as themselves.

More likely, her programs will create a new entitlement for people not in acute distress, while those on the streets will not benefit. That’s nuts.